Heat the oil in a casserole dish and sate the onion and garlic for a couple of seconds to soften slightly. Add the vegetables and sauté for 2 to 3 minutes until golden. Add the beans, stock, wine, passatta and arrowroot, mixed with a little water. bring to the boil, season and simmer for 20 minutes.
Transfer to an individual, or a 22cm, ovenproof dish and sprinkle with the chopped tarragon. For the topping, whisk together the eggs and yogurt, then stir in the cheddar cheese, polenta, flour and baking powder. Spread over the vegetables to make a thick crust and finally sprinkle over the parmesan cheese. Bake for 20 minutes at 200 degrees Celsius until golden. Serve and enjoy.